A raster output scanner (ROS) that can switch between outputs of 240, 300, 400 and 600 spots per inch (spi) by using a 1200 lines per inch addressibility printer and switching the data for each scan on or off at the correct time to create the required density of spots per inch.
Electronic printers are currently single resolution printers, i.e. either 240, 300, 400, etc., spi. The resolution is chosen on the basis of desired copy quality and features for the particular market segment targeted. However, once a resolution is chosen, along with the active image dimensions and photoreceptor speed, the ROS or optical printhead is designed for the particular data rate which will accommodate those particular parameters. The ROS is then limited to that spot density, in the sense that a significant redesign and development cycle must be undertaken to change the resolution or processor speed.
It would be attractive from a customer satisfaction point of view to develop a printer with multiple resolution capability which would be able to interface with scanners having different resolutions, and to print images of different spot densities, even on the same page or during the same raster.
The prior art includes U.S. Pat. No. 4,733,252. This is a dual-beam acousto-optic modulator (AOM) which can be used to generate dual beams for use in this invention. The concept of multi-resolution, however, is not considered.
U.S. Pat. No. 4,780,732. This is a device which allows fast scan interlacing and possible interlace in the slow scan direction while using an electro-optic total internal reflection (TIR) scanner. However, it requires moving focusing apparatus. Again, no scheme for slow-scan multi-resolution for various spot densities is considered.
U.S. Pat. No. 4,806,951. Basically, this patent describes the interlacing requirements for scanning several beams which are not adjacent, i.e., they are separated by much more than one scan line. Again, no mention is made of multi-resolution.
U.S. Pat. No. 4,847,643 describes very basic polygon ROS design equations. It relies on several separate ROS's prepared as "cartridges" to satisfy resolution requirements.
U.S. Pat. No. 4,905,027. LED bar based patent. This can achieve multiple resolution in the slow scan but not in the fast scan. Additionally, it does not have the advantage of direct data transfer from a X spi generated image into a X spi print unless the LED is specifically an X spi LED. Conversion and interpolation is needed.
U.S. Pat. No. 4,907,017 describes how to obtain a dual-beam diode laser ROS. Does not address multi-resolution concepts.
U.S. Pat. No. 4,926,200. This is the closest in intent to this invention. It uses two LED bars: one at a one resolution and the other at another resolution such that it can print two different resolutions on the same page. It can only get as many resolutions as there are different LED bars.
What is required is a system wherein one ROS can switch between different spot densities.